A supersonic aircraft design for cruising efficiently at Mach 2. Engine nacelles are placed under each wing near mid-span. A wedge nose at each nacelle creates oblique shock waves to the sides. The shocks spread horizontally under the wings. The greater pressure behind the shocks pushes up on the wings, creating the phenomenon known as compression lift.
Examples are found in U.S. Pat. No. 3,137,460 by the manufacturer of the XB-70 Mach 3 bomber. Most of the instances are for the XB-70's single, six engine nacelle under the fuselage. Although his FIG. 12 does show an individual engine nacelle under a wing, his conical nose spike 21 wastes half of the shock which spreads downward, away from the wing.
A similar observation can be made for the B-58 Mach 2 bomber (JANE's All the World's Aircraft, 1960-61, page 288.) It has individual nacelles hanging from a delta wing. The round nacelle noses create conical oblique shocks. A small part of a shock spreads under the wing where it creates compression lift, but most of the shock is wasted downward, or upward into thin air ahead of the wing.
The XB-70 Mach 3 bomber aircraft (JANE's, 1968-69, page 341; or 1964-65, page 268) was the first aircraft to achieve large amounts of compression lift. It established the need for a vertical wedge as the first surface of a supersonic air intake. The wedge creates a V-shaped shock wave whose sides trail back at an angle from the nose of the air intake. Being vertical, the wedge creates the oblique shocks horizontally. The shocks are positioned correctly to hug the bottom of the wing located just above the air intake. The pressure rise behind the shocks pushes up on the wings, causing compression lift. The invention aims to do the same, but with separate engine nacelles each housing only two engines. Engine accessibility for maintenance is much improved, important for airline use.
The Concorde Mach 2 airliner has one nacelle under each wing and each nacelle houses only two engines. However, in Concorde the wedge surfaces which create the shock waves are horizontal, not vertical as in ours or XB-70. Horizontal wedges throw the shock wave downward, away from the wing, so they do not generate compression lift.
The second part of compression lift is now addressed. This is trapping the oblique shock's. The XB-70 did it by folding its wingtips downward. They called it the reflected shock effect (FIG. 6 of Paper 650798, Society of Automotive Engineers (“SAE”), also in bound SAE Transactions, Vol. 74, 1966, page 604; Call Number TL1.S6.)
In the invention, the wingtips don't fold down. There are fixed tip fins which can intercept the outboard shocks. Tip fins are already known in the art. That leaves the inboard shocks. Inboard shocks exist because there are two widely separated engine nacelles. The invention uses a narrow keel below the fuselage to intercept the inboard shocks.
If no keel was there, the inboard shocks would just cross and escape under the rear of the aircraft. They would miss out on the reflected shock effect.
Keels in sailboats are thin plates which are cranked down from a centerboard. Our keel is thicker than that. It's wide enough to house the wheel bogies of the main landing gear. The bogies are stored one behind the other, which keeps the keel relatively slim. No example of tandem bogie storage was found in the U.S. Patent literature.
There is a supersonic bomber, The Tu-160, with the required vertical-wedge air intakes (Aviation Week & Space Technology (hereafter, “AWST”) Aug. 24, 1992, page 65, the bottom photo.) The Tu-160SK space launch version (JANE'S, 1998-99, page 443) has a “centreline mount” for the Burlak rocket which is a keel of some kind. The keel is present in the photo of a model (AWST, Jun. 27, 1994, page 75.) The actual keel is seen in the small photo, AWST, Jun. 19, 1995, page 26. This “keel” appears to be a long, slender pylon of small depth, but which is capable of intercepting a little of the inboard oblique shocks caused by the nose wedges of the air intakes. Taking measurements on the large photo on that page 26, the keel is found to be 1.5 mm/8.0 mm=18.8 percent of the depth of the side of the engine nacelle. Thus, only about 19 percent of the depth of the shock's pressure field would be intercepted by this keel. The rest of the shock would pass below the keel and miss the reflected shock effect. Our keel is much deeper, about four feet which is the size of a wheel in the main landing gear. Of course, the Burlak rocket can intercept the whole shock—But then it's a composite aircraft.